Silver Spring, Maryland summary C ' r y s t a l o s c i l l a t o r s u s e d i n o r b i t i n g satellites to provide a working time scale are s u b j e c t t o drifts i n frequency that cannot be predicted more thsrl a few days a t a time. A frequency synthesizer has been developed that w i l l translate t h e i n p u t f r e q u e n c y t o the output frequency according t o precise mathematical formulation. This device provides the means t o conv e r t t h e s a t e l l i t e c r y s t a l o s c i l l a t o r t o a prescribed frequency that w i l l make t h e s a t e l l i t e c l o c k agree i n r a t e t o c l o c k s on t h e ground. A frequency tuning span of 65 parts per m i l l i o n i s covered i n 38 m i l l i o n d i s c r e t e s t e p s . The movemen't a c r o s s t h i s t u n i n g range i n the s a t e l l i t e is c o n t r o l l a b l e from t h e ground e i t h e r t o s p e c i f i c s t e p s o r t o a rate of progression through the steps. Short term i n s t a b i l i t i e s a t t r i b u t e d t o t h e s y n t h e s i z e r have a one sigma deviat i o n o f 1 p a r t i n IOU averaged over 1 second. Technical Description Block Diwram The b a s i c approach t o t h e s y n t h e s i z e r is shown i n t h e s i m p l i f i e d b l o c k d i a g r a m o f F i g u r e 1. The divide by A is a counter that overflows and resets when it reaches a number s t o r e d i n a r e g i s t e r . The a c t i o n o f overflowing generates a d i g i t a l signal whose fundamental frequency is fo/A. T h i s s i g n a l is combined i n a d i g i t a l v o l t a g e c o n t r o l l e d o s c i l l a t o r ( s i n g l e s i d e band mixer) t o generate a d i g i t a l wave form whose sum frequency is:This waveform is divided by B as above and i n j e c t e d i n t o a v e r y c a r e f u l l y b a l a n c e d a n a l o g s i n g l e s i d e band mixer.The output frequency is then:where B i s the course frequency adjustment and A i s the fine frequency adjustment.The r e s o l u t i o n o f t h e device over i t s operating range is shown i n F i g u r e 2. Having i d e n t i f i e d t h e b a s i c s t r u c t u r e , t h e n e x t l e v e l o f d e t a i l is shown i n t h e n e x t b l o c k diagram, Figure 3. Here w e see t h e A and B counters and the two s i n g l e s i d e band mixers. These counters are cont r o l l e d b y t h e c o n t e n t s o f A and B h o l d i n g r e s i s t o r s . By ground command, Command Data Words are i n j e c t e d i n t o t h e Command Data Word holding register. This word c o n t a i n s t h e d a t a f o r a h o l d i n g r e g i s t e r and t h e i d e n t i f i e r as t o where it belongs; A o r B. There is another means provided for control, through the onboard computer interface. Software programs and d a t a i n j e c t e d from t h e ground, permits t n e computer t o r a i s e o r l o w e r t h e v a l u e o f d i v i d e r number A. Provision has been made f o r t h e n m b e r A to operate between two limits 6300 and 13469. liken e i t h e r limit number i...
* Os autores agradecem a colaboração dos Drs. Luis Arcon e Marcos Kísíl, bem com o apoio recebido por parte dos Profs. Drs. Humberto de Moraes Novaes e Carlos J.
A time transfer experiment was carried out between the master clocks of the U.S. Naval Observatory and the U.S. National Bureau of Standards in Boulder, Colorado, using passively recovered Nova satellite time signals at each ground station. Timing correlation of the master clocks derived from the satellite signals agreed with comparisons made by Cs clock transfers within 50 ns.
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